The present invention relates to a process for bonding a body of copper or a copper-chromium alloy to a body of ceramics, and to bonded articles of bodies of ceramics and copper or a copper-chromium alloy.
Heretofore, stout bonding of a copper body to a body of ceramics, e.g., alumina ceramics, especially such stout bonding as is required in a pressure or vacuum envelope, has been performed in accordance with the following process employing the so-called Telefunken method.
First, applied to surfaces to be bonded of alumina ceramics is a metallizing paste, a major component of which is a powdered refractory metal such as Mo or W, which is similar to alumina in coefficient of thermal expansion and sintering properties. Second, the applied layer of the metallizing paste is sintered in an atmosphere of humidified hydrogen gas at near the softening point of alumina, i.e. 1300.degree. C. to 1500.degree. C., to form a compact metallized layer stoutly bonded to the body of the alumina ceramics. Third, the metallized layer is plated with nickel or gold in order to improve the wetability between the outer layer and a molten brazing material. Finally, the copper and ceramic bodies are heated together at a temperature at which the solid brazing material trapped between the surfaces bond with both, and then are slowly cooled, the copper body and the ceramic body thus being bonded stoutly together.
This process for bonding a copper body to alumina ceramics entails some disadvantages as follows:
(1) An expensive metal such as Mo or W must be employed;
(2) The number of process steps is relatively high as an independent metallizing process in which a metal such as Mo or W is employed must be included in the bonding process;
(3) In the metallizing process, a completely sintered alumina ceramic is reheated to a temperature near the softening point of alumina; and
(4) Brazing material must be employed.
In conclusion, the known process for bonding a copper body to alumina ceramics entails such disadvantages as high cost, many difficult-to-control factors and a long process execution time.